If by local, you mean, how do you get Twitter to show your location. You must be using Google Chrome, and enable geolocation via Google Gears. There are a few mobile apps that support it as well. At the moment Twitter's geolocation features are very limited.

Magnitude measures size while direction measures geolocation

There is no such thing as a PHP form. Forms are written in HTML or other client side scripting languages.

Geolocation, environmental factors, human and animal migration, social economics, religion and/or belief system, wealth, politics, trade, and introduction of and availability of ingredients.

Both are geolocation based check-in games, but Foursquare came first and then Gowalla tried to take what foursquare had created and build off it to make it better, but foursquare is still better.